The proposed project will document bone loss in the legs of spinal-cord injured patients, using a sample of 20 individuals with recent spinal-cord injury. The research will evaluate the pattern of bone loss over a 2-year period, after injury. Specifically, the onset of bone loss and the rate of loss will be analyzed. In addition to individual and group comparison over time, the amount of bone loss will be compared to some bone-specific markers. This research should yield information important to the well-being of paralyzed individuals, in addition to data of broader significance and applicability. Precise knowledge of bone-loss rates and patterns (up to .5% precision) will aid in decisions about patient suitability for walking experiments, now becoming more prevalent with advances in the field of functional electrical stimulation. It will also provide a basis for the development of treatment methods for bone loss, either for paralyzed individuals or those who are confined to bed for long periods of time. Finally, the spinal-cord injured patient serves as a model to study the effects of weightlessness in space flight, permitting estimation of maximal duration of space travel without long-term bone loss.